Patent GB-204139-A (GB)
Title: Improvements in or relating to the fore and aft control of aircraft
IPC: G05D1/04
Filed: 1922-06-26
Abstract: 204,139. Vickers, Ltd., and Vickers, O. H. D. June 26, 1922. Hunting and differential; mercury switches.-- The fore and aft control-mechanism of aircraft is automatically actuated bo maintain the aircraft at a constant altitude, through the medium of a statoscope comprising a closed air chamber subjected to atmospheric pressure through a movable septum, such as a mercury globule, the movement of which makes or breaks an electric controlling circuit. The statoscope air-chamber F terminates in a U-tube f, which is open to the atmosphere at its end f<1> and is contracted at the part receiving the mercury globule f<2>, but swells out on either side so that when an ascent or descent is made the globule moves into an enlarged portion of the tube and allows communication between the atmosphere and the chamber F in order to re-establish equality of pressure and prepare the statoscope for further control. Contacts f<3>, f<4>, lead into the tube f at its centre and each side of the globule f<2>, a small displacement of which on either side bridges the contact f<3>, and one of the contacts f<4>, the centre ecntact f<3> is connected to a spring G the end of which carries an adjustable screw g adapted to engage a pin or. one side of an aneroid box J, the other side of which carries a brush j<1> contacting with the edge of a clock disc K, provided at intervals around its periphery with segmental strips k. The gap between the contacts j, g is so adjusted by the contact screw g that when the aircraft reaches a desired height the box J moves the contact against the contact g. The spring G is also movable by means of a screw g<1> and is so set that when the contacts j, g engage a catch j<2> retains them in contact the clock K thereafter at predetermined intervals connects one side of a battery L to the central contact f<3> which if the aircraft is changing its level is connected over the globule f<2> to one of the contacts f<4>, thus completing a circuit for one of two electromagnets H, which through ratchet and pawl mechanism rotate a quick-pitch screw M one step in one or other direction each time a segment K engages the pin j<1>. The screw M carries a contact carrying member N which is thereby moved either to the right or left and at contacts n, d completes a control circuit which initiates a correcting operation in the fore and aft control. Since the position of the contacts d is also variable by the air-pressure controlling boxes C, C', the control is a differential one depending upon variations of both altitude and aerofoil incidence. Closure of a pair of contacts n, d, completes a circuit for a relay R<1> and also for a small reversible electromotor P which rotates a worm-wheel p adapted to be clutched to the shaft q by a magnetic clutch R the circuit of which is completed by the relay R<1>. A downwardly projecting sleeve q<1> on the spindle q is formed with an internal quick-pitch thread screwing on to the controlling shaft o of a variable delivery pump O of the Williams-Janney type connected to a suitable motor unit such as the double-acting ram described in Specification 188,944, with which hunting gear of any known type may be associated. According to which pair of contacts n, d, is closed, the motor P is rotated in one or other direction to raise or lower the controlling shaft o and cause appropriate actuation of the fore and aft control to correct the upward or downward deviation. The circuit of the motor P includes a brush s contacting with a segment on a follow-up commutator Q which rotates with the shaft q, so that when the latter has turned sufficiently to correct the controls, the brush s passes off the segment connected to the contact n engaged by the contact d and opens the motor circuit and the magnetic clutch R. For larger changes of altitude or incidence the contact d engages two adjacent segments on the commutator q and the brush s passes over both segments before the motor P is stopped, thereby permitting a larger correcting movement of the pump-controlling shaft o. When the motor P is stopped and the worm-wheel p declutched, the reaction on the shaft o returns the commutator J to its normal position where it is correctly centred by the engagement of a spring-plunger T in a notch on a ring q<2> on the shaft q. Specification 204,138, [Class 4, Aeronautics], is referred to